1. Field of the Invention
The invention, in general, relates to construction compounds containing a biological fiber and, more particularly, to a compound of the kind conventionally supplied as a dry powder, prepared and applied as a slurry before drying or curing to a hard, stone-like state. While the invention will hereinafter be primarily described in connection with cement, mortar and concrete, it will be understood by those skilled in the art that it is equally useful in connection with such substances as gypsum and plaster of paris or, indeed, organic adhesives and the like.
2. Background of the Invention
In the construction trade it is common practice to reinforce construction compounds such as, for example, mortar, concrete or screed by the addition of artificial or synthetic fibers such as polypropylene. Such additives have been found in certain circumstances to enhance the physical properties of the construction compounds. They may, for instance, result in increased load-bearing and strain-resisting properties of constructed components or surfaces. In Europe, about 10,000 tons of synthetic fibers are used annually as reinforcement for concrete, mortar and screed mixtures. Structures and surfaces made from concrete, mortar or screed without the fiber additives tend to develop cracks from shrinkage or condensation. They are neither durable nor do they tolerate heavy loads.
Disadvantages inherent in the use of chemically produced fibers as reinforcement for concrete and the like are that they are relatively expensive, they are derived from finite raw materials, and they are a burden on the ecology. Moreover, it is difficult to process them in connection with construction compounds of the kind here under consideration. For proper mixing they require complex mixing equipment such as horizontal pan mixers. Experiments conducted by the inventors have shown that adding such fibers to concrete slurries and the like in ordinary tumble mixers results in the formation of lumps. Such lumps detrimentally affect the homogeneity of the mixture as well as the properties of the finished product. The load-bearing properties of components and surfaces made from concrete incorporating such lumped fibers are reduced significantly.
Aside from the use of synthetic fibers, it has also been known to utilize natural fibers for improving the characteristics of artificial stones or masonry. For instance, German patent 298,332 discloses a method of making artificial masonry compounds utilizing jute fibers mixed to a homogenous mass with a hydraulic binder and water. The compound is thereafter formed into a desired shape by stamping or compacting with alternate net-like layers of jute fiber webs.
German Patent specification 3,902,595 proposes the manufacture of construction boards from hydraulic binders as fillers, using cellulose derivatives such as cellulose acetate and the like aside from organic fibers such as wood pulp, paper, flax, hemp, jute. In order to provide for permanent strength of the boards and thus to improve their useful life, the proportion of water soluble sodium, i.e., sodium monoxide (Na.sub.2 O) is reduced to less than 10 mg/10 g of solids. The proportion of water soluble potassium, i.e. potassium oxide (K.sub.2 O) is below 15 mg/10 g of solids. Hence, damage to cellulose fibers from alkaline substances is substantially avoided.
WO 96/25370 A1 relates to a wall plastering compound mixed with natural fibers, for interior and exterior walls. The natural fibers used are hemp or bombax fiber prepared by a degumming process. Large scale production of this building material is not possible, however, since at present degumming or cottonizing of hemp is technically feasable on a laboratory scale only. There are no indications that hemp cottonzing plants are even in their planning stages. Moreover, it is questionable whether sufficient quantities of hemp fibers harvested in the manner described in WO 96/25370 are available. They are harvested at a time at which the blossoms are at the beginning stage of pollenization. That is to say their seeds have not yet ripened, which in some parts of the world, as in the European Union, may be considered to be a deterrent to commercialization as such plants are not subject to government subsidies. Hence, there is only a small, if any, incentive to plant hemp or other textile plants of properties similarly useful in the context of the present invention.